1. Field of the Invention
The invention relates to a sensing method, and more particularly to a sensing method for a touch sensing device.
2. Description of the Related Art
FIG. 1 shows a conventional capacitive touch sensing array. As shown in FIG. 1, a touch sensing array 1 comprises a plurality of sensing electrodes grouped into vertical sensing electrodes and horizontal sensing electrodes which interlace with the vertical electrodes. In FIG. 1, five vertical sensing electrodes V1˜V5 and five horizontal sensing electrodes H1˜H5 are given as an example. When a conductive object, such as a conductive stylus or a finger, touches the touch sensing array 1, a sensing circuit connected to the sensing electrodes can detect the location of the object by measuring changes in capacitances associated with the electrodes and the object. The measured capacitances may be cross-capacitances between interlaced vertical sensing electrodes and the horizontal sensing electrodes or self-capacitances of the respective sensing electrodes. For the two types of the measured capacitances, the values of the capacitances are affected by the presence of the object.
The changes in the capacitances associated with the sensing electrodes can be measured by a charge integrator circuit of the sensing circuit. In order to perform measurement of a cross-capacitance between one set of the interlaced vertical and horizontal sensing electrodes, a charge integrator circuit is connected to the measured vertical sensing electrode. The charge integrated by the charge integrator circuit depends on the value of the corresponding cross-capacitance. At the beginning of the measurement of each set of the interlaced vertical and horizontal sensing electrodes, the charge integrator circuit has to be reset. In order to perform measurement of a self-capacitance of one sensing electrode (one vertical or horizontal sensing electrode), a charge integrator circuit is connected to the measured sensing electrode. The charge integrated by the charge integrator circuit depends on the value of the corresponding self-capacitance. Similarly, at the beginning of the measurement of each sensing electrode, the charge integrator circuit has to be reset. In the two different cases, the process of resetting the charge integrator circuit takes some time, which limits the rate at which the touch sensing array is sensed. Moreover, the process of resetting the charge integrator circuit also generates noise due to charge injection effects.
Thus, it is desired to provide a new scanning method for a touch sensing array to measure capacitances induced by touching.